JP2014080176A - Tire position discrimination system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire position discrimination system capable of deciding shortly with a simple arrangement whether any tire attachment position has been changed.SOLUTION: Tire air pressure detectors 4a to 4d each transmit a tire air pressure signal Stp, in which a gravity component force detected by an acceleration sensor 10 is contained, to a TPMS receiver 12. The TPMS receiver 12 compares a gravity component force, which is received with an IGSW 18 turned off, with a gravity component force received with the IGSW 18 turned on, and decides whether any tire attachment position has been changed before and after the IGSW 18 is turned on or off. If the gravity component forces on all of four wheels of tires 2a to 2d are identical to one another, the TPMS receiver 12 decides that tire attachment positions have not been changed, and displays on a display 16 previous values as the tire attachment positions. If the gravity component force on any of the tires 2a to 2d on the four wheels is different, the TPMS receiver 12 decides that a tire attachment position has been changed, and performs an action of displaying a message "Tire positions are being discriminated" on the display 16 at a driver seat or displaying no tire positions.

Description

  The present invention relates to a tire position determination system that determines the position of each tire required when monitoring the air pressure of each tire.

  In recent years, vehicles tend to be equipped with a tire pressure monitoring system for the purpose of safe driving. The tire pressure monitoring system includes a direct type in which a tire pressure detector is attached to each tire, and the tire pressure is monitored based on a tire pressure signal wirelessly transmitted from each tire pressure detector. The tire pressure signal includes ID (tire ID) written in each tire pressure detector in addition to the pressure data detected by the sensor in the tire pressure detector. Therefore, the vehicle body can identify the air pressure and the tire position of each tire, and notifies the driver of the tire position when a low-pressure tire is present.

  The tire pressure monitoring system has an auto-location function that periodically checks the mounting position of each tire in order to accurately maintain the mounting position of the tire even if, for example, the tire is replaced or replaced with a new tire. . As an auto-location function, for example, a format is known in which each tire house is provided with an initiator (trigger), and the tire pressure detector determines the mounting position of each tire by transmitting the radio wave from the initiator to the tire pressure detector. (For example, refer to Patent Documents 1 and 2).

JP 2006-062516 A JP 2012-126341 A

  By the way, the tire position change should be executed, for example, when the ignition switch is off, that is, when the engine is stopped. Therefore, when the tire position is changed, the next time the ignition switch is turned on, the tire position is changed. Therefore, when the ignition is turned on, it is necessary to quickly determine whether or not the tire position has been changed. There is. As this determination method, for example, an initiator is provided in each tire house, and it is possible to determine whether or not the tire position has been changed by checking the response result by this initiator. There was a problem that required many points.

  An object of the present invention is to provide a tire position determination system capable of determining whether or not the tire mounting position is changed with a simple configuration in a short time.

  A tire position determination system that solves the above-described problem is a function of a direct tire pressure monitoring function that monitors the air pressure of each tire in a vehicle body by a tire air pressure signal transmitted from a tire air pressure detector attached to each tire. In the configuration for determining the position of each tire by identifying the position of the tire pressure detector by a tire position determination function, the gravity information detected by the gravity force detection unit of the tire pressure detector is used as the basis. The characteristic value according to the angle of the tire air pressure detector can be calculated, and the first characteristic value of the tire air pressure detector when the ignition switch of the vehicle is off and the after the ignition switch is turned on A characteristic value acquisition unit for acquiring a second characteristic value of the tire pressure detector; the first characteristic value; Based on the comparison result of the characteristic value comparison unit that compares the characteristic value and the characteristic value comparison unit, whether or not the tire mounting position is changed is determined, and the operation of the tire pressure monitoring function is controlled based on the determination result. And an operation control unit.

  According to this configuration, for example, if the tire position is changed while the ignition switch is off, there is a possibility that the position of the tire air pressure detector in the tire rotation direction has changed when the ignition switch is turned on again. high. Therefore, in the case of this configuration, the first characteristic value when the ignition switch is switched off and the second characteristic value when the ignition switch is switched from off to on are compared. It is determined that the tire mounting position has changed before and after the ignition switch is turned off / on. Therefore, when the ignition switch is switched from OFF to ON, it is possible to immediately determine whether or not the tire mounting position has been changed.

  In addition, since it is determined whether or not the tire mounting position has been changed using the gravity information detected by the gravitational component force detection unit of the tire pressure detector, for example, the tire mounting position can be changed without installing an initiator or the like in each tire house. It is possible to determine the presence or absence. Therefore, it is possible to determine whether or not the tire mounting position is changed with a simple configuration.

  In the tire position determination system, when the operation control unit determines that there is no change in the mounting position of the tire, it is preferable that the previous value of the tire position determination is displayed on the display unit of the tire pressure monitoring function. According to this configuration, when there is no change in the tire mounting position, the previous value obtained by the tire air pressure monitoring function can be used as it is for displaying the tire mounting position.

  As a definition, “previous value” refers to information on a tire attachment position determined immediately before the ignition switch is turned off by specifying the tire attachment position by the tire position determination function while the ignition switch is on.

  In the tire position determination system, when the operation control unit determines that there is a change in the mounting position of the tire, it is preferable that the display unit of the tire air pressure monitoring function is switched to a display notifying that effect. According to this configuration, when there is a change in the tire mounting position, the fact is displayed on the display unit of the tire air pressure monitoring function, so the driver can be notified that the tire mounting position has changed. It becomes possible.

  In the tire position determination system, it is preferable that the operation control unit causes the tire position determination function to re-execute a tire position determination operation when it is determined that the mounting position of the tire has changed. According to this configuration, when there is a change in the tire mounting position, it is possible to update to the correct tire mounting position.

  In the tire position determination system, the tire position determination function performs a tire position determination operation periodically or irregularly even after it is determined that there is no change in the tire mounting position. When recognizing that the position has changed, it is preferable to re-register the tire position and to change the display on the display unit of the tire pressure monitoring function. According to this configuration, even if it is determined that there is no change in the tire mounting position, the tire position determination is performed periodically or irregularly after the ignition switch is turned on. Therefore, if the tire mounting position is changed while the ignition switch is off, even if the tire pressure detectors for all tires take the same position before and after replacement, they will be executed regularly or irregularly when the ignition switch is on. The correct tire mounting position can be re-registered by the tire position determination function.

  In the tire position determination system, the tire pressure detector wirelessly transmits the gravity information constantly or intermittently regardless of whether the ignition switch is turned on or off, and the characteristic value acquisition unit is configured to constantly or intermittently transmit the tire pressure. It is preferable that the gravity information is acquired when the ignition switch is turned off by receiving the gravity information transmitted from the detector. According to this configuration, it is possible to collect gravity information in advance from each tire pressure detector during ignition off. Therefore, even if the vehicle is started immediately after the engine is started, it is possible to determine in advance whether or not the tire mounting position is changed when the ignition switch is turned on, for example, before the start of traveling.

  In the tire position determination system, a combination of the axle rotation speed acquisition unit that acquires the axle rotation speed detected by the axle rotation speed detection unit, and the axle rotation speed and the characteristic value when the ignition switch is turned off is calculated. Based on the combination information, a combination information calculation unit, an information holding unit that holds the combination information obtained by the combination information calculation unit so that the combination information can be continuously used even after the ignition switch is turned off, and the tire is based on the combination information. An expected value calculation unit that calculates an expected value of the axle rotation number and the characteristic value that can be obtained after the rotation, and the characteristic value comparison unit includes the axle rotation number and the acquired value after the ignition switch is turned on. It is preferable to determine whether or not the tire position is changed by comparing the characteristic value with the expected value. According to this configuration, when the ignition switch is turned off, the combination information of the axle rotation speed and the characteristic value is stored in the memory in the tire whose position has been determined, and this information is retained even when the ignition switch is turned off. After the ignition switch is turned on, it is determined whether or not the tire position has been changed by comparing the combination information captured after the tire has rotated and the expected value calculated from the combination information stored in the memory. Therefore, for example, even if the vehicle starts running after the ignition switch is turned on and before the tire pressure detector transmits gravity information, it is possible to determine whether or not the tire position has changed.

  In the tire position determination system, it is preferable that the operation control unit determines whether or not the tire position has changed when calculating the characteristic value for the first time after the ignition switch is turned on. According to this configuration, after the ignition switch is turned on, when the characteristic value is calculated for the first time, it is possible to determine whether or not the tire position has changed, so in a short time after the ignition switch is turned on, It is possible to complete the determination of whether or not the position has been changed.

  In the tire position determination system, the operation control unit determines whether or not the tire position has been changed when receiving the first radio wave transmitted from the tire pressure detector after the ignition switch is turned on. Is preferred. According to this configuration, it is possible to complete the determination as to whether or not the tire position has been changed immediately after the ignition switch is turned on.

  In the tire position determination system, it is preferable that the combination information calculation unit calculates a combination of the axle rotation speed and the characteristic value immediately before the ignition switch is turned off. According to this configuration, the axle rotation speed and the characteristic value may be shifted each time the vehicle stops. However, if the acquisition timing of the combination information is immediately before the ignition switch is turned off, the combination information to be held is a value with less error. It becomes possible to do.

  In the tire position determination system, it is preferable that the combination information calculation unit obtains a plurality of combinations immediately before the ignition switch is turned off, and calculates combination information at the time of ignition off based on the plurality of the combinations. According to this configuration, since the combination information is comprehensively determined and calculated from a plurality of values immediately before the ignition switch is turned off, the combination information can be calculated with high accuracy.

  According to the present invention, it is possible to determine whether or not the tire mounting position is changed with a simple configuration in a short time.

The lineblock diagram of the tire position judging system of a 1st embodiment. The conceptual diagram of the tire pressure detector which can detect a gravity component force. The flowchart explaining operation | movement of a tire position change detection function. The state figure in which the position of a tire air pressure detector changes before and after IG-OFF / ON. The block diagram of the tire position determination system of 2nd Embodiment. The graph which shows the change of each output of the axle shaft rotation speed and gravity component with respect to time passage. (A), (b) is an illustration showing an example of a combination of axle rotation speed and gravity component force. The graph which shows the change of each output of the axle shaft rotation speed and gravity component with respect to time passage. The block diagram of the tire position determination system of 3rd Embodiment. The wave form diagram of the time change of axle speed and gravity component force. The illustration figure of the detector angle of each tire pressure detector.

(First embodiment)
Hereinafter, 1st Embodiment of a tire position determination system is described according to FIGS.
As shown in FIG. 1, the vehicle 1 is provided with a tire pressure monitoring system (TPMS: Tire Pressure Monitoring System) 3 that monitors the tire air pressure and the like of each tire 2 (2a to 2d). In the tire pressure monitoring system 3 of this example, tire pressure detectors 4 (also referred to as tire valves: 4a to 4d) are provided for the tires 2a to 2d, and tire pressure signals Stp detected by the tire pressure detectors 4a to 4d are provided. Is wirelessly transmitted to the vehicle body 5 to directly monitor the tire pressures of the tires 2a to 2d in the vehicle body 5. The tire pressure monitoring system corresponds to a tire pressure monitoring function.

  The tire pressure detector 4 is provided with a controller 6 that controls the operation of the tire pressure detector 4. A tire ID (also referred to as a valve ID) is written and stored in the memory 7 of each controller 6 as a unique ID of each tire 2. The tire air pressure detector 4 is provided with a pressure sensor 8 that detects tire air pressure, a temperature sensor 9 that detects tire temperature, and an acceleration sensor 10 that detects acceleration (rotation) generated in the tire 2. It is connected to the controller 6. The controller 6 is connected to a transmission antenna 11 capable of transmitting a radio wave in the UHF (Ultra High Frequency) band.

  The vehicle body 5 is provided with a receiver (hereinafter referred to as a TPMS receiver) 12 that receives the tire pressure signal Stp transmitted from the tire pressure detector 4 and monitors the tire pressure. The TPMS receiver 12 is provided with a tire pressure monitoring ECU (Electronic Control Unit) 13 that controls the operation of the TPMS receiver 12 and a receiving antenna 14 that can receive radio waves in the UHF band. In the tire 15 of the tire pressure monitoring ECU 13, tire IDs of the respective tires 2a to 2d are written and stored in association with tire positions (right front, left front, right rear, and left rear). For example, a display unit 16 installed on an in-vehicle instrument panel or the like is connected to the TPMS receiver 12.

  As shown in FIG. 2, the acceleration sensor 10 detects a gravity component Gr in the axle direction (tire radial direction) with respect to the gravity G as the gravity applied to the tire air pressure detector 4. The tire pressure detector 4 transmits, as a tire pressure signal Stp, a signal including pressure data, temperature data, gravity component data, and tire ID by UHF. The tire air pressure detector 4 transmits the tire air pressure signal Stp to the vehicle body 5 when the tire 2 enters a rotating state or at regular or irregular intervals with a predetermined time interval, for example. For example, even if it is determined that the tire 2 does not rotate, the tire air pressure signal Stp is transmitted at the same or longer interval than that at the time of rotation. The gravity component Gr is an example of a characteristic value (first characteristic value, second characteristic value), and a tire air pressure signal Stp including gravity component data is an example of gravity information.

  When the receiving antenna 14 receives the tire pressure signal Stp from the tire pressure detectors 4a to 4d, the TPMS receiver 12 checks the tire ID in the tire pressure signal Stp, and if the ID check is established, the same tire pressure signal is obtained. Check the pressure data in Stp. At this time, if the pressure value is equal to or lower than the low pressure threshold, the TPMS receiver 12 displays the low pressure tire on the display unit 16 in association with the tire position. The TPMS receiver 12 performs the tire pressure determination for each tire pressure signal Stp received to monitor the tire pressures of the tires 2a to 2d.

  As shown in FIG. 1, the tire pressure monitoring ECU 13 is provided with an auto-location function unit 17 that determines the front / rear / left / right mounting positions of the tires 2 a to 2 d as one function of the tire pressure monitoring system 3. In the case of this example, the tire position determination method (auto-location method) in the auto-location function unit 17 is arbitrary, but the acceleration sensor 10 capable of detecting the gravitational component force Gr is mounted on the tire pressure detector 4 as in this example. In this case, it is preferable to adopt a tire position determination method using the gravity component Gr. A specific tire position determination method is disclosed in, for example, “Japanese Patent Application No. 2011-209509”. The auto location function unit 17 corresponds to a tire position determination function.

  The auto-location function unit 17 determines whether or not the tire mounting position has changed before and after the ignition switch 18 is turned on / off based on the gravitational force Gr detected by the acceleration sensor 10 (tires). Rotation detection function). As described above, whether or not the tire position is changed before and after the ignition switch 18 is turned off / on is because the position of the tire rotation or the like should be changed when the engine is stopped with the ignition switch 18 turned off. This is because the positions of the tires 2a to 2d can be changed when the ignition switch 18 is turned on again.

  In this example, the tire air pressure monitoring ECU 13 includes an ignition state monitoring unit 19 that monitors the switch state of the ignition switch 18 based on the ignition switch signal output from the ignition switch 18, and the gravitational force component in the tire air pressure signal Stp. A gravity component acquisition unit 20 that acquires data is provided. When the gravitational component force acquisition unit 20 receives the tire pressure signal Stp transmitted from the tire pressure detector 4 by the receiving antenna 14, the gravity component force Gr is read by reading the gravity component data in the tire pressure signal Stp. To get. The gravitational component force acquisition unit 20 acquires the gravitational component force Gr for the four wheels of the tires 2a to 2d when the ignition switch 18 is turned off and when the ignition switch 18 is turned on. The ignition state monitoring unit 19 and the gravitational component force acquisition unit 20 are examples of the characteristic value acquisition unit.

  The tire pressure monitoring ECU 13 includes a gravitational component force Gr (Gr1) detected by each tire pressure detector 4a to 4d when the ignition switch 18 is turned off, and each time when the ignition switch 18 is switched from off to on. A gravity force comparison unit 21 that compares the gravity force (Gr2) detected by the tire pressure detectors 4a to 4d is provided. The gravity component comparison unit 21 checks whether or not the gravity component Gr has changed before and after the ignition switch 18 is switched from OFF to ON in all the tire pressure detectors 4a to 4d. The gravity component comparison unit 21 is an example of a characteristic value comparison unit.

  The tire pressure monitoring ECU 13 is provided with an operation control unit 22 that determines whether or not the mounting positions of the tires 2a to 2d are changed based on the comparison result of the gravity force comparison unit 21 and controls the operation of the tire pressure monitoring system 3. ing. If the gravity components Gr of all the tires 2a to 2d are the same before and after the ignition switch 18 is switched from OFF to ON, the operation control unit 22 determines that the tire position has not changed, and displays the previous value as the tire position as it is. Displayed on the unit 16. Further, the operation control unit 22 determines that the tire position has changed if the gravity component Gr is changed even if the tires 2a to 2d are one wheel before and after the ignition switch 18 is switched from OFF to ON, and the display unit 16 Is displayed as “tire position determination in progress”, or the tire position is not displayed.

Next, the operation of the tire position change detection function of this example will be described with reference to FIGS. 3 and 4.
In step 101 shown in FIG. 3, the gravitational component force acquisition unit 20 determines whether or not the ignition switch 18 is off based on the monitoring result of the ignition state monitoring unit 19. That is, it is determined whether or not the engine of the vehicle 1 is stopped. At this time, if the ignition switch 18 is off, the process proceeds to step 102, and if the ignition switch 18 is not off, the process waits at step 101.

  In step 102, the gravitational component force acquisition unit 20 acquires the gravitational component force Gr1 for the four wheels of the tires 2a to 2d when the ignition switch 18 is OFF. At this time, since the tire pressure detectors 4a to 4d transmit the tire pressure signal Stp at their own radio wave transmission timing, the gravitational component force acquisition unit 20 detects each tire pressure signal at the timing of receiving each tire pressure signal Stp. Gravity component force Gr1 of the containers 4a to 4d is acquired.

  In step 103, the gravitational component force acquisition unit 20 stores the gravitational component forces Gr1 for the four wheels of the tires 2a to 2d acquired in step 102 in the memory 15 of the tire air pressure monitoring ECU 13.

  In step 104, the gravitational component force acquisition unit 20 determines whether or not the ignition switch 18 is turned on based on the monitoring result of the ignition state monitoring unit 19. In other words, it is determined whether or not the power state of the vehicle 1 has been operated from OFF to ACC ON or IG ON, for example. If the ignition switch 18 is on, the process proceeds to step 105. If the ignition switch 18 is not on, the process waits at step 104.

  In step 105, the gravitational component force acquisition unit 20 acquires the gravitational component force Gr2 for the four wheels of the tires 2a to 2d when the ignition switch 18 is on. Also at this time, since the tire pressure detectors 4a to 4d transmit the tire pressure signal Stp at their own radio wave transmission timing, the gravitational component force acquisition unit 20 receives each tire pressure signal Stp at the timing of receiving each tire pressure signal Stp. Gravitational component force Gr2 of the detectors 4a to 4d is acquired.

  In step 106, the gravity component comparison unit 21 compares the gravity component Gr1 and the gravity component Gr2. Here, if the gravitational component forces Gr1 and Gr2 are the same in all four wheels of the tires 2a to 2d, the routine proceeds to step 107. On the other hand, if even one of the tires 2a to 2d has different gravitational force components Gr1, Gr2, the routine proceeds to step 108.

  In step 107, when the gravity components Gr1 and Gr2 are the same for all four wheels before and after the ignition switch 18 is switched from OFF to ON, the operation control unit 22 displays the previous value as the tire position on the display unit 16 of the driver seat. indicate. In other words, the operation control unit 22 causes the auto location function unit 17 to normally operate and displays the previous value of the tire attachment position on the display unit 16. Here, since the rotation of the tires 2a to 2d, the change to the new tire, and the like were not performed, it can be said that there is no change from the tire position specified before the ignition switch 18 is turned off. There is no problem even if the previous value of the tire position is displayed on the display unit 16 as it is.

  Incidentally, as shown in FIG. 4, after the ignition switch 18 is turned off, for example, when the positions of the tires 2a to 2d are rotated or changed to new tires, the tire air pressure is changed before and after the ignition switch 18 is turned off / on. The positions of the detectors 4a to 4d in the tire rotation direction should change. Therefore, at this time, since Gr1 and Gr2 do not coincide with each other in the determination in step 107, the process proceeds to step 108 in the determination in step 107.

  In step 108, when the gravity components Gr1 and Gr2 are different even in one wheel before and after the ignition switch 18 is switched from OFF to ON, the operation control unit 22 displays a message “Now determining tire position” on the driver seat display unit 16. Is displayed. Note that the action taken by the action control unit 22 at this time is not limited to displaying “determining tire position”, and may be an action not displaying any tire position.

  In step 109, the operation control unit 22 outputs an autolocation execution request to the autolocation function unit 17 and causes the autolocation function unit 17 to perform autolocation. Therefore, even if the tires 2a to 2d are rotated or changed to new tires, the correct tire position is re-registered in the tire pressure monitoring ECU 13.

  By the way, when “determining tire position” is displayed on the display unit 16 in step 108, the previous value of the tire position may be displayed on the display unit 16. This is because the user can recognize that the tire position is not accurate even if the previous value of the tire position is displayed on the display unit 16 if there is a display “determining the tire position”. .

  For example, if the tire rotation position changes because the vehicle body 5 is deliberately pushed while the ignition switch 18 is off, it is determined that the tire 2 has rotated before and after the ignition switch 18 is turned off / on, and the tire Although the position change of 2 is not performed, “tire position determination in progress” is displayed on the display unit 16. However, in this case, the same tire position as the previous value is calculated in the auto location determination executed during the display of “determining tire position”. Therefore, even in such a situation, it can be said that there is no problem in displaying the previous value of the tire position when “tire position determination in progress” is displayed.

  Note that the auto-location operation is periodically executed even in a situation where it is determined that the mounting position of the tire 2 has not changed. This is because it is assumed that the positions of the tire pressure detectors 4a to 4d are all the same by chance before and after the ignition switch 18 is switched off / on. Therefore, even after it is determined that the attachment position of the tire 2 has not changed, the correct tire position can be specified by continuously executing the auto-location operation.

  Further, in the tire position changing function of the present example, it is necessary to store the gravitational component force Gr of the four tires 2a to 2d in the memory 15 of the tire air pressure monitoring ECU 13 immediately after the ignition switch 18 is turned off. Here, “immediately after” refers to the time from when the vehicle body 5 is jacked up until the tires 2a to 2d are rotated. Therefore, the gravitational force Gr acquired “just before” the ignition switch 18 is turned off may be used. Here, “immediately before” refers to a time that is short enough that the tire position cannot be changed by jacking up after the gravitational force Gr is acquired and before the ignition switch 18 is turned off.

  Further, when the ignition switch 18 is turned on, the TPMS receiver 12 acquires the gravitational component force Gr from the tire pressure detectors 4a to 4d again, but some users start running immediately after turning on the ignition switch 18. It is preferable that the gravitational component force Gr is acquired at all times or intermittently while the vehicle is stopped (including a case where the reception is continued for a certain period of time or when a radio wave is received for a short time). In this way, even if the ignition switch 18 is turned on and the vehicle starts running immediately, it is possible to determine whether or not the tire position has changed before the vehicle starts running.

According to the configuration of the present embodiment, the following effects can be obtained.
(1) Each tire pressure detector 4a-4d includes the gravitational component force data detected by the acceleration sensor 10 in the tire pressure signal Stp and transmits it to the TPMS receiver 12. The TPMS receiver 12 acquires the gravitational force Gr1 when the ignition switch 18 is off and the gravitational force Gr2 when the ignition switch 18 is on, and compares them to determine whether the ignition switch 18 is off / on. It is determined whether or not the tire mounting position has been changed before and after. The TPMS receiver 12 determines that the tire mounting position has changed if at least one of the four tires 2a to 2d has different gravitational force Gr before and after the ignition switch 18 is turned on / off. Operations such as “determining the tire position” or not displaying the tire position on the seat display unit 16 are performed.

  Therefore, in this example, when the ignition switch 18 is turned off and when the ignition switch 18 is turned on, the gravitational component force Gr is collected from the tire pressure detectors 4a to 4d, and the ignition switch 18 is turned on. Since it is determined whether or not the tire mounting position has been changed by checking whether or not the gravity force Gr has changed before and after turning off / on, the tires can be used for a short time after the ignition switch 18 is turned on. The determination as to whether or not the mounting position has been changed can be completed. In addition, since it is determined whether or not the tire mounting position is changed using the gravity force Gr detected by the tire pressure detectors 4a to 4d, for example, whether or not the tire mounting position is changed without installing an initiator or the like in each tire house. Can be determined. Therefore, it is possible to determine whether or not the tire mounting position is changed with a simple configuration.

  (2) When it is determined that there is no change in the tire mounting position when the ignition switch 18 is turned on, the tire mounting position obtained in the previous tire position determination is displayed on the display unit 16, so the previous value is used as it is. Can be used to display.

  (3) When it is determined that the tire mounting position has changed when the ignition switch 18 is turned on, for example, “determining the tire position” is displayed on the display unit 16 or nothing is displayed on the display unit 16. Notify the driver to that effect. Therefore, it is possible to notify the driver that the tire mounting position has been changed while the ignition switch 18 is turned off.

  (4) When it is determined that the tire mounting position has been changed when the ignition switch 18 is turned on, the tire mounting position is re-determined by the tire position determination function. Therefore, even if the attachment position of the tires 2a to 2d is changed when the ignition switch 18 is turned off, the changed tire attachment position can be re-registered in the tire pressure monitoring ECU 13.

  (5) Even when it is determined that there is no change in the tire mounting position when the ignition switch 18 is on, the tire position determination function continues to check the tire position in the operation under the ignition-on condition. Therefore, when the tires 2a to 2d are changed in position, even if the tire pressure detectors 4a to 4d of all the tires 2a to 2d take exactly the same position before and after the replacement, they are finally registered as correct tire mounting positions. Can be reworked.

  (6) The tire air pressure detector 4 may transmit the gravity component Gr constantly or intermittently while the vehicle 1 is stopped. For this reason, the gravity force Gr can be collected from each of the tire pressure detectors 4a to 4d while the ignition switch 18 is turned off. Therefore, even if there is a user who starts the vehicle 1 immediately after the engine is started, the determination of whether or not the tire mounting position has been changed can be made in advance before the start of traveling.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIGS. 2nd Embodiment is an Example which changed the determination method of the tire position change presence / absence of 1st Embodiment. Therefore, the same parts as those in the first embodiment are denoted by the same reference numerals, detailed description thereof is omitted, and only different parts are described in detail. Note that the tire rotation function is executed, for example, when it is determined that the vehicle 1 is stopped.

  As shown in FIG. 5, the vehicle 1 is provided with an axle rotation speed detection sensor 32 (32a to 32d) for detecting the rotation speed of each axle 31 (31a to 31d) of the tires 2a to 2d. As the axle rotation speed detection sensors 32a to 32d, for example, an ABS (Antilock Brake System) sensor is used. For example, the axle rotation speed detection sensors 32a to 32d detect a plurality of teeth (for example, 48) attached to the axles 31a to 31d by the sensing unit on the vehicle body 5 side, thereby generating a rectangular wave pulse signal Spl as TPMS. Output to the receiver 12. The axle rotation speed detection sensors 32a to 32d output, for example, “96 pulses” as detecting both rising and falling of the pulse per one rotation of the tire. The axle rotation speed detection sensor 32 is an example of an axle rotation speed detection unit.

  The tire pressure monitoring ECU 13 is provided with an axle rotational speed acquisition unit 33 for acquiring the number of pulses of the pulse signal Spl output from the axle rotational speed detection sensors 32a to 32d of the axles 33a to 33d, that is, the axle rotational speed N. Yes. The axle rotation speed acquisition unit 33 acquires the axle rotation speed N for each of the axles 31a to 31d.

  The tire pressure monitoring ECU 13 includes a combination information calculation unit 34 that acquires combination information (correlation) Dk of the axle rotation speed N and the gravity component Gr of each tire pressure detector 4a to 4d, and tire position determination (auto-location determination). In the tires 2a to 2d in which the ignition switch 18 is turned off, the combination information holding unit 35 that holds the combination information Dk immediately before the ignition switch 18 is turned off in the memory 15 is provided. The combination information calculation part 34 calculates | requires the combination information Dk in each tire air pressure detector 4a-4d. The combination information holding unit 35 holds the combination information Dk stored in the memory 15 in the memory 15 continuously even after the ignition switch 18 is turned off. The tire air pressure monitoring ECU 13 is expected to calculate the expected value of the combination of the axle rotation speed N and the gravitational force component Gr, which is assumed based on the rotation of the tires 2a to 2d after the ignition switch 18 is turned on. A value calculation unit 36 is provided. The tire pressure monitoring ECU 13 is provided with a combination information comparison unit 37 that compares the combination information Dk newly acquired after resumption of traveling with the combination information Dk calculated from the combination information Dk stored in the memory 15. The combination information comparison unit 37 is an example of a characteristic value comparison unit.

  The operation control unit 22 performs tire position determination based on the gravity component data in the tire pressure signal Stp received from the tire pressure detectors 4a to 4d at the first stop after the ignition switch 18 is turned on. . For example, the operation control unit 22 confirms in each tire pressure detector 4a to 4d whether or not the combination of the axle rotation speed N and the gravity component Gr acquired after the ignition switch 18 is turned on takes an expected value. Determine whether the tire position has changed.

  Next, operation | movement of the tire position change detection function of this example is demonstrated using FIGS. Here, it is assumed that the tire position determination has been completed, and it is assumed that, for example, ID1 is the ID of the right front tire.

  As shown in FIG. 6, the combination information calculation unit 34 acquires the gravitational component force Gr periodically transmitted from the right front tire pressure detector 4a. The combination information calculation unit 34 confirms the axle rotation speed N of the right front axle rotation speed detection sensor 32a at that time, and obtains combination information Dk of the axle rotation speed N and the gravity component Gr. The combination information calculation unit 34 calculates combination information each time the gravitational component force Gr is acquired from the right front tire pressure detector 4a.

  When the ignition switch 18 is switched off, the combination information holding unit 35 stores the combination information Dk immediately before turning off (even when it is off) in the memory 15 and holds it. As a result, the combination information Dk remains stored in the memory 15 even after the ignition switch 18 is turned off.

  FIG. 7 shows an explanatory diagram of the correlation between the axle rotation speed N and the gravity component Gr. As shown in FIG. 7A, for example, when the tire air pressure detector 4 is positioned at the apex (0 o'clock) in the tire rotation direction, assuming that the axle rotation speed N is “10”, for example, FIG. If the tire pressure detector 4 is positioned at the bottom (6 o'clock) in the tire rotation direction, the axle rotation speed N should be “58 (= 10 + 48)”. Thus, there is a correlation between the axle rotation speed N and the gravitational force component Gr, and this correlation is always established unless the position of the tire 2 is changed.

  As shown in FIG. 6, when the ignition switch 18 is turned on for the first time (point P1), for example, the right front tire pressure detector 4a stops at the bottom point (6 o'clock) in the tire rotation direction, and the gravitational component force It is assumed that the tire pressure signal Stp including data is wirelessly transmitted to the vehicle body 5 by the tire pressure detector 4a. The gravitational component force acquisition unit 20 reads that the gravitational component force Gr of the tire air pressure detector 4a is “−1G” from the right front tire air pressure signal Stp received at this time. Further, the axle rotational speed acquisition unit 33 also captures “58” as the axle rotational speed N of the right front axle rotational speed detection sensor 32a at the point P1.

  By the way, the expected value calculation unit 36 calculates an expected value that is assumed to be taken after the right front tire 2a rotates based on the combination information Dk held in the memory 15. Therefore, the combination information comparison unit 37 determines whether or not the tire position has been changed by comparing the combination of the axle rotation speed N and the gravity component Gr acquired at the point P1 with the expected value. At this time, the operation control unit 22 determines that there is no change in the tire position if the axle rotation speed N and the gravitational force Gr at the P1 point match the expected values, and conversely if it does not match, the operation control unit 22 changes to the tire position. Judge that there was.

  When the operation control unit 22 confirms that all four wheels are as expected, the four wheels recognize that the tires 2a to 2d are not rotating while the ignition switch 18 is off. Therefore, the operation control unit 22 displays the previous value as the tire position on the driver seat display unit 16. On the other hand, if even one of the four wheels does not meet the expected value, the operation control unit 22 recognizes that the tire position has been changed while the ignition switch 18 is off. Therefore, the operation control unit 22 outputs an autolocation execution request to the autolocation function unit 17 and causes the autolocation function unit 17 to perform autolocation.

  FIG. 8 shows an example of a method for determining the tire position at an early time (point P0) after running after the ignition switch 18 is turned on. In this case, the tire air pressure detector 4 has a function capable of determining whether or not the vehicle 1 is stopped. The determination of whether or not the vehicle stops is made when the vehicle 1 is stopped when there is no change in the gravitational force Gr for a certain period of time (for example, 10 minutes or more). The tire pressure detector 4 wirelessly transmits a tire pressure signal Stp including the measured gravitational force component Gr when determining that it is the first run after the vehicle stops. Then, the TPMS receiver 12 uses the gravity component Gr in the tire air pressure signal Stp to determine whether or not the tire position has changed.

  Note that this tire position change presence / absence determination pattern is an operation that is executed during traveling. Therefore, the tire pressure signal Stp transmitted at this time needs to include, for example, information indicating that the own signal is a signal used for checking whether or not the tire position is changed.

  Further, in the case of the second embodiment, the combination information Dk is a combination immediately before the ignition switch 18 is turned off. However, the combination information Dk is not necessarily obtained immediately before the ignition switch 18 is turned off. Normally, the pulse signal Spl of the axle rotation speed detection sensor 32 and the sensor output of the acceleration sensor 10 may be shifted each time the vehicle stops. However, if the ignition switch 18 is just before being turned off, it is difficult to integrate errors. This is because accurate determination is possible. However, the error often depends on the accuracy of the acceleration sensor 10.

  Therefore, the combination information Dk may be calculated by comprehensively judging from a plurality of pieces of information immediately before the ignition switch 18 is turned off, for example. As a specific example of this processing, for example, there is an average processing that takes an average of a plurality of times. As another example, there is a weighting process (fuzzy process) for weighting each value for a plurality of times. In the weighting process, the error-absorbed combination information Dk is calculated by setting, for example, 50% immediately before (1 previous), 30% 2 previous, 20% 3 previous, and 10% 4 previous.

According to the configuration of the present embodiment, the following effects can be obtained in addition to (1) to (6) described in the first embodiment.
(7) When the ignition switch 18 is turned off, the combination information Dk of the axle rotation speed N and the gravity component Gr immediately before the ignition switch 18 is turned off is stored in the memory 15, and the ignition switch 18 is turned on again. Continue to use after being used. After the ignition switch 18 is turned on, the combination information Dk acquired after the tires 2a to 2d have rotated and the expected value calculated from the combination information Dk stored in the memory 15 are compared to determine whether the tire position has changed. To do. If the combination information Dk acquired after turning on the ignition switch 18 matches the expected value, it is determined that there is no change in the tire position, and even if one wheel does not match, it is determined that the tire position has been changed. Therefore, even if the vehicle 1 starts running immediately after the ignition switch 18 is turned on and the transmission of the gravity component Gr is not in time, it is possible to determine whether or not the tire position has changed.

  (8) After the ignition switch 18 is turned on, the gravitational component force Gr is wirelessly transmitted from the tire pressure detectors 4a to 4d to the TPMS receiver 12 at the first stop, and the tire position is changed using the gravitational component force Gr. Determine presence or absence. Therefore, it is possible to complete the determination of whether or not the tire position has been changed within a short period of time of the first stop after the ignition switch 18 is turned on.

  (9) The combination information Dk held in the memory 15 is information associated immediately before the ignition switch 18 is turned off. Therefore, the axle rotation speed N and the gravitational force component Gr may be shifted each time the vehicle stops. However, if the combination information Dk is acquired immediately before the ignition switch 18 is turned off, the combination information Dk stored in the memory 15 is retained. Can be a value with less error.

  (10) If a tire position determination radio wave is transmitted from the tire pressure detectors 4a to 4d to the TPMS receiver 12 for the first run after stopping, the determination of whether or not the tire position has changed can be completed immediately. . Therefore, the driver can be notified immediately of the determination result of whether or not the tire position is changed after the start of traveling.

  (11) The combination information Dk stored in the memory 15 may be obtained by comprehensively judging (average processing, weighting processing, etc.) from a value immediately before the ignition switch 18 is turned off. In this case, the combination information Dk can be calculated with high accuracy.

(Third embodiment)
Next, a third embodiment will be described with reference to FIGS. The third embodiment is an improved invention of the second embodiment, and this example will be described only for parts different from the second embodiment.

  As shown in FIG. 9, the controller 6 of each tire pressure detector 4 includes a peak detector 41 that detects the peak of the gravitational force Gr, that is, the tire pressure detector 4 is at the pole position in the tire rotation direction. And a peak information transmission unit 42 for notifying the TPMS receiver 12 of the peak information Spk when the gravitational force Gr reaches a peak. The peak detector 41 of this example detects, for example, the minimum value of the gravitational component force Gr, that is, the tire air pressure detector 4 being at the apex (position “12 o'clock”) in the tire rotation locus. The peak information Spk is a kind of signal including a command for notifying that a peak has been taken, a tire ID, and the like. For example, when the peak information transmission unit 42 determines that the vehicle speed has become low based on the amount of change in the gravity component Gr, the peak information transmission unit 42 wirelessly transmits the peak information Spk. The peak detection unit 41 and the peak information transmission unit 42 are examples of characteristic value acquisition units, and the peak information Spk is an example of gravity information.

  The tire pressure monitoring ECU 13 is provided with a peak information acquisition unit 43 that acquires peak information Spk transmitted from the tire pressure detectors 4 a to 4 d in the TPMS receiver 12. The tire pressure monitoring ECU 13 stores the axle speed Cn (n = 1 to 4) of the representative wheel 45 every time the peak information Spk is received from each tire pressure detector 4a to 4d, and the axle speed Cn of all the wheels. Then, based on these and the axle rotation speed Cref of the representative wheel 45 at that time, a detector angle calculation unit 44 for obtaining the detector angle θk of each tire air pressure detector 4a to 4d is provided. The detector angle θk is an example of a characteristic value (first characteristic value, second characteristic value), and the peak information acquisition unit 43 and the detector angle calculation unit 44 are examples of a characteristic value acquisition unit.

  FIG. 10 shows a waveform diagram of changes over time in axle rotation speed and gravity component force. In the case of this example, the axle rotation speed Cn (n = 1 to 4) of the representative wheel 45 when the gravitational force Gr reaches a peak (position of “12:00”) is read. For example, when ID3 (for example, the right rear tire pressure detector 4c) is at the “12:00” position, the axle rotation speed C1 of the representative wheel 45 is “13”, and ID2 (for example, the left front tire pressure detector 4b) is “ When the position is “12:00”, the axle speed C2 of the representative wheel 45 is “27”, and when ID1 (for example, the right front tire pressure detector 4a) is the “12:00” position, the axle speed of the representative wheel 45 is When C1 is “40” and ID4 (for example, the left rear tire pressure detector 4d) is in the “12:00” position, the axle rotation speed C4 of the representative wheel 45 is “71”.

  After the axle rotation speeds C1 to C4 of the representative wheel 45 are aligned at “12:00” in all the tire pressure detectors 4a to 4d, an arbitrary determination timing, for example, the axle rotation speed Cref of the representative wheel 45 becomes “83”. Then, the detector angle θk of each tire pressure detector 4a-4d is calculated. The arbitrary determination timing may be after a predetermined time after the axle rotation speeds C1 to C4 of all the four wheels are aligned, or may be any moment when the last axle rotation speed Cn of the four wheels is acquired.

  As shown in FIG. 11, the detector angle θk of each tire pressure detector 4a to 4d is an angle advanced by a predetermined pulse from the “12 o'clock” position. When the pulse of the representative wheel 45 is “83” at an arbitrary determination timing, ID3 is 262.5 degrees (= (83-13) × 360/96) with the position of “12 o'clock” as a reference (0 degree). Become. ID2 is 210 degrees (= (83-27) × 360/96) with the position of “12 o'clock” as a reference (0 degree). ID1 is 161.25 degrees (= (83-40) × 360/96) with reference to the position of “12 o'clock”. ID4 is 45 degrees (= (83-71) × 360/96) with the position of “12 o'clock” as a reference.

  When the four-wheel tire pressure detectors 4a to 4d have finished calculating the detector angle θk, the combination information calculation unit 34 calculates the axle rotation speed C of each axle rotation speed detection sensor 32a to 32d at the moment when the angle calculation is completed. As the reading and combination information Dk, a set of the detector angle θk and the axle rotation speed C in each wheel is calculated. Each time the combination information calculation unit 34 receives new peak information Spk for four wheels and recalculates the detector angle θk, the combination information calculation unit 34 calculates the combination information Dk. When the ignition switch 18 is switched off, the combination information holding unit 35 stores the combination information Dk immediately before being turned off (even when it is turned off) in the memory 15.

  It is assumed that the ignition switch 18 is turned on again and the vehicle 1 resumes traveling. During this traveling, the operation control unit 22 compares the initial combination information Dk calculated after resuming traveling with the expected value obtained from the combination information Dk stored in the memory 15 to determine whether the tire position has been changed. Judge whether or not. If the combination information Dk matches, the operation control unit 22 determines that there is no change in the tire position, and conversely if it does not match, the operation control unit 22 determines that the tire position has changed if it does not match.

According to the configuration of this embodiment, in addition to (1) to (11) described in each embodiment, the following effects can be obtained.
(12) In the case of the determination method of this example, the detector angle θk is set to the gravitational component force Gr detected by the acceleration sensor 10 even if an error or temperature tolerance caused by the centrifugal force generated during tire rotation occurs. It can be accurately determined. Therefore, it is possible to accurately determine whether or not the tire position has changed.

  (13) Since the determination of whether or not the tire is changed is executed at a low speed, the peak information Spk transmitted from the tire pressure detectors 4a to 4d is less likely to collide. For this reason, the determination of the presence or absence of tire changes can be completed in a short time.

(14) Since it is not necessary to stop the vehicle to determine whether or not the tire has changed, the detector angle θk can be determined at a desired timing that can be regarded as a low speed.
Note that the embodiment is not limited to the configuration described so far, and may be modified as follows.

  In each embodiment, the tire pressure detector 4 may take an operation of transmitting the tire pressure signal Stp when the acceleration sensor 10 detects that the rotation of the tire 2 has stopped, for example.

  In each embodiment, the tire air pressure detector 4 is not limited to transmitting the detected gravitational force component Gr in the tire air pressure signal Stp, and may transmit only the gravitational force component Gr alone, for example.

  In each embodiment, the tire position determination function determines the position of the tire pressure detector 4 from the magnitude of the received signal strength (RSSI) when the TPMS receiver 12 receives the tire pressure signal Stp, for example. It can be changed to other methods such as a method of specifying.

In each embodiment, Gr1 acquired as the gravitational force at the time of ignition off may be data collected immediately before the ignition switch 18 is turned off, for example.
In each embodiment, the acceleration sensor 10 may be a two-axis detection type capable of detecting both the gravity component force Gr in the axle direction and the component force in the vertical direction of the gravity component force Gr.

  In each embodiment, determination of the switch state of the ignition switch 18 may be performed based on a signal input from another member such as a body ECU that manages the power source of the vehicle electrical component. In short, any signal that can be used to determine whether the engine has stopped can be substituted for other signals in addition to the ignition signal.

-In each embodiment, the operation | movement performed after the judgment of the presence or absence of a change of a tire attachment position is not limited to the operation | movement which controls the display of the display part 16, and can be changed into another operation | movement.
-In each embodiment, judgment of the presence or absence of a change of a tire attachment position is not restricted to the system which confirms all four wheels of tire 2a-2d, What is necessary is just to confirm at least 1 wheel.

In the second and third embodiments, the actually measured combination information Dk and the expected value are not limited to perfect coincidence, and some error may be allowed.
In each embodiment, the radio wave transmitted from the tire air pressure detector 4 at the time of resuming traveling is not limited to the tire air pressure signal Stp, and may be a dedicated radio wave for tire position change determination, for example. This signal includes at least gravity component data, tire ID, and the like.

  In each embodiment, the acceleration sensor 10 is not limited to a sensor that detects the gravitational force component Gr in the axle direction, and may be a sensor that can detect only the gravitational force force in the direction orthogonal to the axle direction, or the axle direction and its orthogonality. A biaxial sensor that can detect both gravitational force components in the direction may be used.

In each embodiment, the gravitational component force may be a component force in a direction orthogonal to the component force in the axle direction.
In each embodiment, the gravity component detection unit is not limited to the acceleration sensor 10, and various sensors can be adopted as long as the sensor can detect the gravity generated in the tire air pressure detector 4.

-In each embodiment, an axle rotation speed detection part is not limited to an ABS sensor, If it is a sensor which can detect the rotation speed (rotation amount) of the axle 31, it can change into another sensor.
-In each embodiment, the stop determination in the vehicle 1 can be performed based on the vehicle speed data output from meter ECU etc., for example.

-In each embodiment, determination of the presence or absence of a tire position change may also include a spare tire.
In each embodiment, the previous value determination is not limited to being performed when the vehicle is parked or parked, and may be performed at a low speed that can be regarded as a parked vehicle, for example.

In each embodiment, the automatic location determination (for example, calculation of the detector angle θk) can be changed to various modes as long as it uses a gravitational component force.
Next, the technical idea that can be grasped from the above embodiment and other examples will be described below.

  (A) In the tire position determination system, the characteristic is a gravitational component force detected by a gravitational component force detection unit of the tire pressure detector, and the characteristic value acquisition unit is configured to turn off the ignition switch. The first gravitational component force and the second gravitational component force obtained after the ignition switch is turned on are obtained.

  (B) In the tire position determination system, the tire pressure detector includes a characteristic information notification unit that wirelessly transmits the characteristic information to the receiver when the gravity detection unit detects the characteristic of gravity. The value acquisition unit uses the axle rotation speed of the representative wheel when the characteristic information is received by the receiver and the axle rotation speed of the representative wheel at a certain timing, and is detected by each tire pressure detector as the characteristic value. A detector angle is obtained, and a first detector angle when the ignition switch is off and a second detector angle after the ignition switch is turned on are obtained.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 2 (2a-2d) ... Tire, 4 (4a-4d) ... Tire pressure detector, 5 ... Vehicle body, 16 ... Display part, 17 ... Auto location function part as a tire position determination function, 18 ... Ignition Switch, 19 ... Ignition state monitoring unit constituting characteristic value obtaining unit, 20 ... Gravitational component force obtaining unit constituting characteristic value obtaining unit, 21 ... Gravitational component force comparing unit as characteristic value comparing unit, 22 ... Operation control unit , 31 (31a to 31d) ... axle, 32 ... axle rotation speed detection sensor as an axle rotation speed detection unit, 33 ... axle rotation speed acquisition unit, 34 ... combination information calculation unit, 35 ... holding combination information as an information holding unit , 36 ... expected value calculation unit, 37 ... combination information comparison unit constituting the characteristic value comparison unit, 41 ... peak detection unit constituting the characteristic value acquisition unit, 42 ... pipes constituting the characteristic value acquisition unit Information transmission unit, 43... Peak information acquisition unit constituting the characteristic value acquisition unit, 44... Detector angle calculation unit constituting the characteristic value acquisition unit, Stp... Tire pressure signal constituting gravity information, G. (Gr1, Gr2) ... gravity component, N (N1, N2), C (Cn, C1 to C4, Cref) ... axle speed, θk (θk1, θk2) ... detector angle, Spk ... constituting gravity information Peak information, Dk ... combination information.

Claims (11)

This is one function of a direct tire pressure monitoring function for monitoring the air pressure of each tire in the vehicle body based on a tire pressure signal transmitted from a tire pressure detector attached to each tire. In the tire position determination system that determines the position of each tire by identifying with the position determination function,
A characteristic value according to the angle of the tire pressure detector can be calculated based on the gravity information detected by the gravity component detection unit of the tire pressure detector, and the tire pressure detection when the ignition switch of the vehicle is off A characteristic value acquisition unit for acquiring a first characteristic value of the container and a second characteristic value of the tire pressure detector after the ignition switch is turned on;
A characteristic value comparison unit for comparing the first characteristic value and the second characteristic value;
An operation control unit that determines whether or not the mounting position of the tire is changed based on a comparison result of the characteristic value comparison unit, and that controls an operation of the tire air pressure monitoring function based on the determination result. Tire position determination system. 2. The tire according to claim 1, wherein when the operation control unit determines that there is no change in the mounting position of the tire, the previous value of the tire position determination is displayed on a display unit of the tire air pressure monitoring function. Position determination system. The said operation control part switches the display part of the said tire pressure monitoring function to the display which notifies that, when it judges that the attachment position of the said tire has changed, The display which notifies that. Tire position determination system. The said operation control part makes the said tire position determination function re-execute the operation | movement of tire position determination, when it is judged that the attachment position of the said tire has changed, The any one of Claims 1-3 characterized by the above-mentioned. The tire position determination system according to item. The tire position determination function performs a tire position determination operation periodically or irregularly even after it is determined that there is no change in the tire attachment position, and recognizes that the tire attachment position has changed in this operation. Then, the tire position determination system according to any one of claims 1 to 4, wherein the tire position is re-registered and the display of the display unit of the tire pressure monitoring function is changed. The tire pressure detector wirelessly transmits the gravity information constantly or intermittently regardless of whether the ignition switch is on or off,
The said characteristic value acquisition part acquires the said gravity information at the time of the said ignition switch OFF by receiving the said gravity information transmitted from the said tire pressure detector normally or intermittently. The tire position determination system according to any one of 5. An axle rotation speed acquisition unit for acquiring the axle rotation speed detected by the axle rotation speed detection unit;
A combination information calculation unit that calculates a combination of the axle rotation speed and the characteristic value when the ignition switch is turned off;
An information holding unit that holds the combination information obtained by the combination information calculation unit so that the combination information can be continuously used even after the ignition switch is turned off;
Based on the combination information, an expected value calculation unit that calculates an expected value of the axle rotation speed and the characteristic value that can be taken after the tire rotates,
The characteristic value comparison unit determines whether the tire position has changed by comparing the axle rotation speed and the characteristic value acquired after the ignition switch is turned on with the expected value. The tire position determination system according to any one of claims 1 to 6. The tire position determination system according to claim 7, wherein the operation control unit determines whether or not the tire position has changed when the characteristic value is calculated for the first time after the ignition switch is turned on. The said operation control part performs the determination of the presence or absence of the change of the said tire position, when the radio wave which the said tire pressure detector transmitted initially after turning on the said ignition switch is received. The tire position determination system described in 1. The tire position according to any one of claims 7 to 9, wherein the combination information calculation unit calculates a combination of the axle rotation speed and the characteristic value immediately before the ignition switch is turned off. Judgment system. The combination information calculation unit acquires a plurality of combinations immediately before the ignition switch is turned off, and calculates combination information at the time of ignition off based on the plurality of combinations. The tire position determination system according to claim 1.